The present invention relates to a magnetic trip assembly and, more particularly, to a magnetic trip assembly for use in an electric circuit breaker.
Many types of electric circuit breakers employ a magnetic trip assembly for providing instantaneous tripping action in response to short circuits or high current overloads. One common type of magnetic trip assembly employs a magnetic member and an armature physically connected with the magnetic member and adapted to coact with a pole face of the magnetic member parallel to the magnetic plane of the magnetic member. When an excessive amount of current passes through a load conductor coupled to the magnetic member, a strong magnetic field is established in the magnetic member in the air gap between the armature and aforementioned pole face, causing the armature to be drawn through the air gap into physical contact with the pole face ("closed" position). An actuating member engaged with the armature moves together with the armature and causes a trip member (e.g. a trip bar) connected with the actuating member to move (e.g., rotate). The movement of the trip member in turn causes a release or unlatching of the latch mechanism of the circuit breaker. The above-described magnetic trip assembly normally employs a spring connected between the magnetic member and the armature for use in returning the armature to its "open" position after operation, and another spring connected between the magnetic member and the trip member for use in returning the trip member to its latched position after operation.
While the above-described magnetic trip assembly operates in a generally satisfactory manner, it nonetheless has certain shortcomings. A principal shortcoming is that the mechanical advantage achieved between the armature and the trip member of the magnetic trip assembly is somewhat limited by virtue of the particular arrangement of the armature and the actuating and trip members and the use of a pole face which is in the same plane as the magnetic plane of the magnetic member, despite the fact that the magnetic field is strongest in the air gap between the armature and the aforementioned pole face. Further, the above-described magnetic trip assembly has a relatively high component count, includes a number of parts having critical dimensions, and requires a large number of machining and assembly operations, thereby leading to increased manufacturing costs and reduced reliability.